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Hi, after finishing my build, it is time to give back to the community and describe the best i can all that i have done.

What you will see here is nothing new of what is already done, if anyone wants to build something similar, adjusted to the specific need of the Portuguese electric company, that defines some crazy periods  for low rate tariff, what needs to be done to count €/kWh is right here.

So lets begin:

First of all in order to know how everything works i ordered a emonTx V2 Kit and a RPI RF receiver from the store, assembled it and learned the inner works of it for some days. BUT somehow i managed to convince myself that 3 CT were not enough, and because i have ethernet right next no my fuse box, there was no need for the wireless stuff.

So a custom build was the solution, with:

- Arduino MEGA 1280
- 1x Voltage sensor (ADC 0)
- 8X CT Analog channels (ADC 2,3,5,6,8,9,11,12)
- Burden resistor of the CT at 68 OHM to increase resolution at 0-50AMP (i have máx 25 Amp at home)
- Ethernet with ENC28J60

I already had most of the parts laying around, only had to buy the transformer and the resistors and condensers for the analog input circuit. Even the inputs terminals were here - that's why i ditched the phone connectors - if you do not have a strong reason to do the same please don't do it!

Here it is front side

and back side
(the high voltage is protected with a big layer of hot glue)

Installed on the fuse box

The input circuit is the same as what is explained in the building blocks for the arduino, however how the whole system is powered is absolutely critical to get good measurements. You can see here (http://openenergymonitor.org/emon/node/10111) some really good advices on how to get proper power. My system is powered through a home alarm system that provides stable 12V. The 12V is stepped down to 7,5V with a DC/DC converter to power the arduino via DC IN. the arduino regulator outputs 5V for the board and feeds another external regulator that provides 3.3V to the ethernet chip. This way was the one that generated the least heat for the whole system and at the same time provided good reference and good measurements.

One problem i have is that CT channels 1, 4 and 7 have higher noise than the rest. They can go up to 20W without a CT attached to the circuit. The others CT channels 2,3, 5, and 6 are really really quiet, they read between -0.2W and 0.2W and average nicely to 0W.

this is the sketch running on the arduino mega, nothing new, reports direcly to emoncms and has some thresholds to get rid of the noisy readings

/*
  EmonTx CT123 Voltage NanodeRF example
  
  Part of the openenergymonitor.org project
  Licence: GNU GPL V3
  
  Author: Trystan Lea
*/

#include "EmonLib.h"
//#define DEBUG
int node_id = 12;

#define NSENSORS 8
EnergyMonitor emon[NSENSORS];                   // Create  instances for each CT channel

//---------------------------------------------------------------------
// The PacketBuffer class is used to generate the json string that is send via ethernet - JeeLabs
//---------------------------------------------------------------------
class PacketBuffer : public Print {
public:
    PacketBuffer () : fill (0) {}
    const char* buffer() { return buf; }
    byte length() { return fill; }
    void reset()
    { 
      memset(buf,NULL,sizeof(buf));
      fill = 0; 
    }
    virtual size_t write (uint8_t ch)
        { if (fill < sizeof buf) buf[fill++] = ch; }
    byte fill;
    char buf[250];
    private:
};
PacketBuffer str;

//---------------------------------------------------------------------
// ETHERNET
//---------------------------------------------------------------------
#include <EtherCard.h>

static byte mymac[] = { 0x74,0x69,0x69,0x2D,0x30,0x31 };   // ethernet interface mac address, must be unique on the LAN
byte Ethernet::buffer[700];
unsigned long timer = 0;
char website[] PROGMEM = "emoncms.org";                    // 1) Set this to the domain name of your hosted emoncms - leave blank if posting to IP address 
static byte hisip[] = { 192,168,1,10 };                    // or if your posting to a static IP server:
boolean use_hisip = false;                                 // change to true if you would like the sketch to use hisip
char basedir[] = "";                                       // 2) If your emoncms install is in a subdirectory add details here i.e "/emoncms3"
char apikey[] = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";        // 3) Set to your account write apikey 
int ethernet_error = 0;                                    // Etherent (controller/DHCP) error flag
int ethernet_requests = 0;                                 // count ethernet requests without reply                 
int dhcp_status = 0;
int dns_status = 0;

//---------------------------------------------------------------------
// SETUP
//---------------------------------------------------------------------
void setup() 
{
  dhcp_status = 0; dns_status = 0; ethernet_requests = 0; ethernet_error=0;

#ifdef DEBUG
  Serial.begin(9600);
  Serial.println("OpenEnergyMonitor.org");
#endif

  delay(1000);
  
  if (ether.begin(sizeof Ethernet::buffer, mymac, 53) == 0) {
#ifdef DEBUG
    Serial.println( "Failed to access Ethernet controller");
#endif
    ethernet_error = 1;
}
 
  delay(1000);
  
  // Ain 1,4,7 e provavelmente 10 induzem ruido
  
  emon[0].current(2, 28.234);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[0].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

  emon[1].current(3, 28.136);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[1].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

  emon[2].current(5, 28.577);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[2].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

  emon[3].current(6, 28.346);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[3].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

  emon[4].current(8, 28.143);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[4].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

  emon[5].current(9, 28.507);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[5].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

  emon[6].current(11, 28.320);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[6].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

  emon[7].current(12, 28.330);         // Calibration factor = CT ratio / burden resistance = 2000 / 68 Ohms = 29.412
  emon[7].voltage(0, 206.3, 1.7);     // (ADC input, calibration, phase_shift)                              

}


//---------------------------------------------------------------------
// LOOP
//---------------------------------------------------------------------
void loop() 
{ 
  dhcp_dns();   // handle dhcp and dns setup - see dhcp_dns tab
  ether.packetLoop(ether.packetReceive());

  if ((millis()-timer)>10000) {  // 10000 = a post every 10 seconds.
    timer = millis();
    
  for (int i=0; i<NSENSORS; i++) {   // perform measurements
    emon[i].calcVI(20,2000);
  }
    
     // Available properties: ct1.realPower, ct1.apparentPower, ct1.powerFactor, ct1.Irms and ct1.Vrms
 
    str.reset();
    str.print(basedir); str.print("/input/post.json?"); str.print("apikey="); str.print(apikey); str.print("&node=");  str.print(node_id);
    str.print("&json={V:"); str.print(emon[0].Vrms); str.print(",");
    str.print("P1:"); abs(emon[0].realPower) < 10 ? str.print("0") : str.print(emon[0].realPower); str.print(",");
    str.print("I1:"); str.print(emon[0].Irms); str.print(",");
    str.print("pF1:"); str.print(emon[0].powerFactor); str.print(",");    
    str.print("P2:"); abs(emon[1].realPower) < 0.9 ? str.print("0") : str.print(emon[1].realPower); str.print(",");
    str.print("P3:"); abs(emon[2].realPower) < 0.9 ? str.print("0") : str.print(emon[2].realPower); str.print(",");
    str.print("P4:"); abs(emon[3].realPower) < 20 ? str.print("0") : str.print(emon[3].realPower); str.print(",");
    str.print("P5:"); abs(emon[4].realPower) < 0.9 ? str.print("0") : str.print(emon[4].realPower); str.print(",");
    str.print("P6:"); abs(emon[5].realPower) < 0.9 ? str.print("0") : str.print(emon[5].realPower); str.print(",");
    str.print("P7:"); abs(emon[6].realPower) < 20 ? str.print("0") : str.print(emon[6].realPower); str.print(",");
    str.print("P8:"); abs(emon[7].realPower) < 0.9 ? str.print("0") : str.print(emon[7].realPower);    
    str.print("}"); str.print("\0");  //  End of json string
#ifdef DEBUG
    Serial.print("Data sent: "); Serial.println(str.buf);
#endif
    ether.browseUrl(PSTR("") ,str.buf, website, 0);  // Send data to the server

  } //end of main 10 second cycle
} // end of main loop

So everything smooth, but again i was not happy with this, had to get cost per kWh, with the real rates depending on the time of the day so read the forum and got the needed help, use addons on the emoncms or use crontab. I still did't setup properly a home server with emoncms (working on that) so crontab was my only choice. My NAS is awake 24x7, so it was easy to make it work. Too bad i'm not able to install emoncms on it.

The Portuguese Electricity company is really creative in setting the offpeak periods, on my case its everyday from 00:00 to 07:00, but on Saturday it gets really twisted. It bounces back and forth between offpeak and onpeak and has different periods if we are in the summer or if we are in the winter.

this is a possible solution that is working for a month now (removed absolute paths to make it easier to read):

New feed with 3 values:

- euro - tariff value in €/kWh
- vazio - if offpeak: 1 otherwise 0
- cheio - if offpeak: 0 otherwise 1

My crontab:

# Bi-horario semana:
0  0    * * 1-5   root   tarifa.sh vazio
0  7    * * 1-5   root   tarifa.sh cheio

# Bi-horario domingo:
0  0    * * 0      root  tarifa.sh vazio

# Bi-horario sabado:
0  0    * * 6     root   tarifa.sh vazio
0  9    * * 6     root   tarifa_verao.sh cheio
30 9    * * 6     root   tarifa_inverno.sh cheio
0  13   * * 6     root   tarifa_inverno.sh vazio
0  14   * * 6     root   tarifa_verao.sh vazio
30 18   * * 6     root   tarifa_inverno.sh cheio
0  20   * * 6     root   tarifa_verao.sh cheio
0  22   * * 6     root   tarifa.sh vazio

the argument in each call is the €/kWh, so every time the tarrif changes i only have to update these files:

# more vazio
0.120294
# more cheio
0.224213

the script itself is very simple and has two variants: one that runs at summer time and one that runs at winter time:

# more tarifa.sh
#!/bin/sh
set -e    # exit if any error
i=$(<$1)  # load file

# Determine the tariff period from the ending of the argument
cheio=0; vazio=0;
if  [[ "$1" == *cheio ]]; then cheio=1; else vazio=1; fi;

curl -s "http://emoncms.org/input/post.json?json={euro:$i,cheio:$cheio,vazio:$vazio}&apikey=XXXXXXXXXXXXX&node=1"

# more tarifa_inverno.sh
#!/bin/sh
set -e    # exit if any error
i=$(<$1)  # load file

# Determine the tariff period from the ending of the argument
cheio=0; vazio=0;
if  [[ "$1" == *cheio ]]; then cheio=1; else vazio=1; fi;

if date +%Z | grep BST &> /dev/null; then   # summer time
:
else                                    # winter time
curl -s "http://emoncms.org/input/post.json?json={euro:$i,cheio:$cheio,vazio:$vazio}&apikey=XXXXXXXXXXXX&node=1"
fi

# more tarifa_verao.sh
#!/bin/sh
set -e    # exit if any error
i=$(<$1)  # load file

# Determine the tariff period from the ending of the argument
cheio=0; vazio=0;
if  [[ "$1" == *cheio ]]; then cheio=1; else vazio=1; fi;

if date +%Z | grep BST &> /dev/null; then   # summer time
curl -s "http://emoncms.org/input/post.json?json={euro:$i,cheio:$cheio,vazio:$vazio}&apikey=XXXXXXXXXXXXXX&node=1"
fi

on emoncoms this is the input feed for the onpeak/offpeak periods:

And this is the general input configuration for the CT's:

With all this it was easy to generate the following graphs:

Brief to see in the smartphone

Detail to debug

Offpeak(Green) and Onpeak(Orange) usage - got this snapshot at midnight, all the counters were set to 0. I can assure you it works though!

and several usage statisticas and costs

The values don't add up nicely in the last picture because i made mistakes at the beginning. It would be nice if we could reset all the feeds to start over.

Well that's it, hope you enjoy and if you are not sure about building your own i hope you find here some arguments to go for it!

Thanks!